Speech-transmitting mechanism.



'eliminate mechanical vibration at the.

UNITED .sire-rus PATENT OFFICE.

sLWooD enrssmenn, oF BUFFALO, NEW Youn; Assienon To Anneleen TELEPHONE am). rnnnennrn confirmar, A conronnfrron on NEW Yonx.

SPEEGHBANSMITTING MEOHANISM.

Spectlcation of Letters' Patent.

A Patented'Nov. 21, 1916.

Application Bled September 17,11914. Serial No. 862,132.;

To all whom' may cof/wem:

Be it known that L'ELWOQD 'Gnissnacnnu ncitizen of the United States, vresiding et Buffalo, Erie county,au d State of New York, have 'invented the following described Improvements in SpcochfTransmt- Ating Mechanism.

The invention is an improvement in means forfaithfully. reproducing as .xiiech'anical vibrations; the complex frequency wave forms such as erecliaracteristic of human roi'e waves, and is particularlyapplicable tof 'telephonie transmission of speech.

By my present invention,the resilience leyer element, to 'impart a high natural frequency or pitch to the vibretory systel'n 'of .the mechanism,'s\1ch as will avoid the'.

,necessity of vibration at said naturalffrequency and thereby 'Substantially elii'ilnateV all 'distorting effects` such-as .are now-polnnionly produced by mechanicalresonance o'E such'.I devices or their mechanical elements.

. An important feature otiny in'veln the discovery that .it is ,poss'ihle to ural frequency, withoi'lt ina-king the nati-lial ,t'requency above the luni't'oi audllnlity' nor anywhere near that high; nor need it even 1I`i'\."-. frequency slightly .hut substantially lalici-ie vthe highest resonant frequency 'oi-the vowel he above the limit of' frequencies important to human speech, provided' the frequencies.

selected he substantially ahov'e the highest resonant frequencies .of thevv'owel sounds. ct, onen'ery lnuctical embodiment-.bf infenton; involves selecting. anatuiva'l sounds. Such 'a.- deviccfw'hile nere-r. effech tively excited at-its naturalfreque ncy,' can he desic'ned to causejju. sliffht magnification.

of the higher vowel frequencieswhich will be progressii-'ely greater'as the frequencies are .higher .and :hence nearer the resonant frequency. Such magnification is admira` h ly adapted 4for correct-ing the distortion (lue to 'apactxm long transmission lines,

i\'l1icl1,..asA is well .lcuowxu operates toattenua'te the lng-lierfrequen'cics more rapidly than .the lower freqluincies.. Inother wor-ds, -while' avoidingtl'i'e distortion which. results where the natural 'frequency oi? mechanical vibration is the samcfas' 'a'v prominent. human voice. vfrequency,l may, iu certain eases.. ntlhze the graduated."magniiylng'eii'ectfof.

-torsional pivot isnpplicd through a4 approaching, .though still suhstentielly .die tf1-nt, mechanical resonance, tomechenically compensate for the reversely graduated,

losses due to the electrical defectsyof the' 'what below 150 periods per second to somewhat above 2000 periods per secondi 'With in unplitude.I

correspoi'iding variations There are eight fundamental vowel 'sounds which are representedby the f' words 'be' .9. gloom, pit, no, pet, raw, mat, father', and?" which comprise the entire Hinge ofA the Gif; sential sounds of articulate .speech. Harvmonic analysis ofthe waves o tvowel sounds showsthat for each vowelshund,.there'1'e a. fundamental Afrequencyfwhiwhccntr'ols'the pitch. Superposed 4v'upoi'r 'thi undame'ntal are anuniber of'overtones or harmonics, and

'these control the quality. 'At t e saine time, between the-fundamental :ind the highest observable harmonic', there. is found a' 'point' ont-he scale'o frequencies, where the intensity oit the sound "ijerymuich'greater than 'at any other poiiit'on pietre-Q; quencies. Thispoint may be'te'rmed e'pont or region of resonance. There is'thus aresl' na nce region. for enclivowel, whichis probchly due` to jthe shape 'of the mouth vcavity through which thefsound passes. 4

I' hare ascertained 'tha-t the regions 'of resonance of .the different vowel sounds oc- Scale oi' frequencies and that the'-r eg'ion-'oi uttering the sound, whether it he 'a In'an,A

woman or child. The .fundamental of, a' particular vowel sound spoken vby a;- man of.'

low pitch roicemay 'he found at 125vpeii'ot'isper second and tlieregion of resonance of' about the th harnujnic. The'i-undaniental. otthlsamevowelsound spoken byv a woml.

periods per second or between the 3rd and -'tli harmonic. The region of resonance of a vowel sound is that region on the scale of frequencies where is found that part of tho-composite sound which is oflthegreatu est intensity, and it is hence the principal factor in speech transmission. he said, as some. may have thought, that-the -important frequencies of speech transmission are represented-hy any particular liar monic, because., as stated above, the fundaniental ofaparticular vowel sound may be found at various different points for differ ent speakers and the harmonics accordingly, while the region of resonance of that vowel sound will always he found at about the saine point on the scale'. Finally, I have asian-tained that the lowest. region of resonance of any vowel soundisataboutORP.

S., and the highest region of resonance,

of any vowel sound at about 1000 P.' P. S., and that 4if an instrument for transmitting or translating speech waves bc so constructed orniodfied as to possess a natural frequency which is very high and at or somewhat above the maximum of this range, it will transmit or translate the waves without distortion, and I have disclosed and claimed such an instrument in .pending applications filed by me on April 27th. 1910,

. Serial No. 558,045. and Maynard' 191i,

peater when thev fundaniental frequency of' the vihratory element is about 1000 P. I. S.:

for transmitters of telephones it should be about the saine', 4but -it is of no consequence if highencxcept that the higher frequencies are more dliicultly obtained and preserved.'

To moet' lthis requirement the mass or inertia of the vibrating system may reduced or the stiffness increased', or both. Variations in the inertia of the movable system or of the stiffness (elasticity) of the parts comprising the; movable system, will canse corresponding variations in the sensitivencss of the device. 'The sensitiveness with4 which any vibrating system responds. to :t given exciting' force is l.urea-ter, the smaller its mass or inertia and` the less the stiffness (elasticity), and .it is therefore desirable to obtain the required high fundamental frequency for the vibrating system by reducing its mass rather-than increasing its'st'i'ness,

It cannot.

the elimination' of distortion being tht prime object, but the reduction of the mass is' of course limited by the practical necessities of construction requiring simplicity and perinanency of adjustment.

In. the accompanying drawings forming part hereof, I' have illustrated the application of a member subject to torsion as a mea-ns of imparting a high natural freqiieiicy to vibratory systems, which without' it would have a frequency so lorir as seriously to distort the transmitted waves.'

l Figure 1 illustrates the use of such torsion members' on a iepeatcr of the kind referred to in the la plications above' mentioned, the parts not cirectly related to the vibratory system being indicated more or lessconventionally; Fig. 2 is a top plan of thepai't's of Fig. 1; Fi Bmrrsection lon line IIL-III of Fig. 1; ifis s Bectionon line IV-IV of Fig. v3; ig. 5 a. longitudinal section through the torsion member; Fig. 6 illustrates the application of a torsion member to an Vordinary speaking. transmitter, thel parts being shown in section, Fig. 7 is a section of' F ig. 1 on line VII- VII of Fig. 6; Fig. S is a perspective detail of the form of torsion member shown'in'Figs. 6 and 7 Figs'. 9 and 10 are details Vof the leverand the bracket as used in Figs' and 7.

Referring first to the simpler structure*- the transmitter-as shown in Fig. 6, etc., the clianibered basel of the transmitter carries a pair of brackets 2 (Fig. 9) lwhich are se'- curely screwed to it with their sockets in alinemen t.` VThe rod 3 is fitted 'snugly into the sockets of lthese brackets and is secured tliercinby srrcivs l. VBetween the brackets the rod supports an arm. or lever 5, for

which purpose it is enlarged at its center, as.

iiidicated'at 6 in Fig. 8, and the hub of the lever lits the enlargement tightly and is secured fast thereon by a set screw or otherwiso. vThe 'attachment .of thearts inencell is held b'y a bracket 10 Screwed' to they back of the base or frame, the cell itself be ing conveniently disposed in an ,aperture 'in'such frame. Intermediate of its ends' the lever 5 is connected with the diaphragm 11 of the transmitter, such connectionjalso being s. firm one such as caribe had by means i of the stem 12 screwed and locked to the lever and clamped to the diaphragm lby a pair of nuts 12* or otherwise.y The da? phragmi clamped t0 thfle'me'by a ringemployed to this end. Depending` upon'the i-naterial. of which the rod is made7 its diamnut and is inclosed andprotected by a cover` bearing-the mouth-piece of the transmitter,

but' it might be supported solely by the lever if preferred. The rear of-the iframe4 is also closed by 'a'oasing with a' hinge lug by means of which the Whole device may be mounted onan' appropriatestand or supprt.

The rod 3 is th'ctorsion member, held securely at both ends inthe brackets 2, and the vibratory movement of its. lever arm takes'place' about the axis of such rodv as a center and againstthe said members 'elastic 'resistanch to torsional displacement, that is to say, the lever arm can be'move'd only' by .15;

slightly twisting the tvvo short sections of the' rod which intervene betweentlie proximate 'faces .of the brackets andfleverihub portion. The construction of. the member is desirably such' that only the part ci. the rod intermediate the brackets is subject to torsion, and various different means 'may be eter and the amount of length subject to torsion maybe greater or less', but for hardened steel, -which 'maybe assumed to he the materialof the rod 3, the proportions shown are about correct', and'its elasticv characteristics under torsional vibration 'aresuch that the whole vvibratory system of the transmitter, includingdiaphragm, and the moving parts" of the microphone cell, is Vthereby raised in 'pitch-'to aihi'gh natural. 'frequency equal to or ahovethehi heat resonance-po- !riod of vowel sounds. i uch system trans. 1 mits the voice iva'ves, or'translates them into.

'electrical waves, without observable distcc? tion. The. natural frequency of the torsional part or parts of the rod alonevibrat1 n.

torsionally, is of course extremely. high and ltem taken' alone, that `Ais to say, volf 'this dia. plragm itselandits connections .with the cell, 'vvhich would have a very lov;r natural period, but -When the high torsional -fre-f qucncy is applied to the other parts ltpron duces a resultant vfr equency sufficiently' high to 'give the results above explained-nud notwithstanding the mass and inertia of diaphragm. l. yInorder that the torsion rod shall gnot vibratejby lateral bending, both of its ends are supported in the'.lc rackel'.'s ,.as above described, and, further,` to guard against of the brackets and lever :hubfbut not so as vtol-restrict'the torsion-.Which 'takes .place Within tliem.- 'The lever -arm 5,-although aplie'aring large .infp'roportion to 'the rod,

is nevertheless of very slight'mass, being bending", the sleeves 13 are litted snugl y thereon between the proximate perpendicular faces made' of aluminum. or 'analloy of alumininn and'formed with thin deep ribs which make' it substantially rigid and' non-flexing ,to

forces of any m'a'gn itude l likely to 1occur in' instruments off-this hind. I preferito maire.

.the'lever out of thecommon aluminum'alloy known as duro-aluminum` inasmuch as that partlcular composition aii'ords substanti ally the stiffness of hardened steel but without the. weight.

In the form shown, the lever is of the second class, the actuating force being applied between therod ulcrui'n or axis .and the microphone connection, which gives some magnification of the amplitude of the motion, but it will beI evident that it might be a lever of' any class and arranged to give any degree of amplification. or. uone'at all,

according to .circumstances and as will. now

be evident. Such a lever and torsion mem ber may be applied to eliminate distortion in various different kinds of apparatus and to other devices operated by oscillating enf orgy represented by 'speech or sound, provided 'only that thetorsonalefrequency is 4selected to givethe WholeA vibratory system ofthe device the desired natural frequency of about 1000 P. P. S., as above er: lained.

It is preferable thatv such. system Wil itselfr 'havejbut a singleresonance period below v2000 P. P. S. l have applied'sueh a torsion .member in this way to the vibratory system of a recording phonograph with marked improvement in the result.

Each of the'above described mechanical details is of 'importance `because of the Well known, but none the .less phenomenal sensitiveness of the microphone cells, diaphragms,. and thev humanl ear in connection 'with which they are used. l'nsuch connection, there is special' significance in the light --but 'wonderfully rigid levercon'struction as v'well' as the absolute lixity of the.axis of vibration .of the lever and.- of the are Aor' vibiatouof the freeen'd thereof, all in` suring a 'perfect single natural -vibratory period, the frequency 'of `which may be easily made .as high as. desirable in'practice, without unduly. shortening :the 'amplitude 'of the vibration, or sacrificing' sensitiveness and efliciencyof functioningoi". the device '--for its` ultimate' purpose;

"The advantages of the construction will be evident when contrasted with ther'present commercial telephone instruments. in these, it has been found wholly iinpracti nl lto use 'levers ofany hind and. eventl'ie sim- `ple diaphragm. instruments that .are used,

Alll) ternal .cause-S' olf distortion are far' '1nore fatal than in transmitters or receivers.

Figs; 1 to 5 illustrate the application cfa preferred' form of torsion member to Eli a telephone rcpeaten The repeater structure includes a transmitter mechanisim, as ahove'descrihoiltand comprises a relativel massiie' base of nonmagneti material Witt a Substantial frame 14 secured thereon and supporting a double-acting microphone cell. The latter comprises n central' fixed electrotle l5 nml two opposite. movable elecl trorles'll', both. electro-plated with platinum nml provided uitlnholes in their faces and haring the. Space between them partlv illecl with grzlmular carbon. The movable electrodos are mechanically connected by a coutral stein 1T passing' through' a hole in thev fixed .electrode and through the granulerontaining chamber, but are insulated from nach other h5' au interposed insulating; Section which forms a positive mechanical connec-tion hotween'lhe two enil portions of the stem. The .tum und movable electrodes are insulated from theveasng bj* means of' the thin :septum .mills 1S to which they are damped h y/ menus of nuts thrriulrfl outhe ruil. These wallsinay he of thm insulating or tloitihle material, mica, forinstanee, aud the stem is threaded so that the electrodes ma;v hu clamped thereon as indicated. The' emlf; of the stoms each rariy an armature ISL which is also iight iuweight, and' in froutofraeh armature there is mounted an eli-iftrommguvt the magnetic. 'lielrll whereof' is noutrolled hy the telephonie current luctuatiuns iu he repeated.' 'The ruils ofthcse l magneteA arl-1 connectml iumultiph` with the. seiuliugl line` hut in opposite-rlirretions, so that a rurront. wa've trilliugvto m'rease the magnetic Iirlil' olf one magnet n'ill'flimiuish that ol the othrl-a ml rice versa. .'.lhe two halves: `ol' tlu louhle microphone: (fell are rounvotril in ,l'liu'luilrrs or branches of the litlurl-mini primary rrruit of nu induction ruil. the srromlary whereof yis 'connu-teil with thu outgoing ,line` assh'own inthe diagram. ln order to reflue-o the weighiiofthe vilnatmfr slwf'strm-tnwnrtl or tothe absolute minimumrequisito 4for a maximum eliiriontgr, the armature 1U is :Formed asa ring seated in a cirrumferrutal rahbet groove Vin a hacking :2 0 whith mayV hma'dei of." almuimim and is.1 1 'o'fei' :1l.ily of4 the'dur umana oia. set of. bolts,' onef of which. ap*

pvars :11:23. The rings 221' form the support or rigidbase Vfor the torsionally vibrating momia diameter lso an 'tol foi the stemul i 0in.V

members of this form of the'.,ir'nientioxt As shown more clearl)r in; 53 Toto t, thotor-v sion member consists jgof -i a! 'single ,pi or block forinedj. withY VSquared{eds 24:,-by means of w'hiehit m'ayrgbell'red'dii'etly to the face of the' ringm I" relatively hea-ry bolts 9.5,'. one pagsinftihroli heu'ch soun red' and and screwed v j' t1`ghtly mto" 'the ring, 'serre fthis -purpo'se .I 'Between the squared ends the, lilo'cltv@orapiecel iSifolfmed w 1th relative i enla iggnznie'nb` for? connection to the. lever arm' '26', fsuchl enlargement repre- Seating Athe hubfof the' lereifbtlbein in faut uu integral part'ofjtl etoA i Between the lever hub .'andvtlie squn'refd."` taclnnentenil, the'itiembenj" "d 0i curved posti;-;7,;the'erossiseetiI l which is flu-ther 'retluoocl h'ybo 'gthe niemher longitudinally .rlinieaoh ir f'f v g5 throughthe posta.' asjadiatd1nt-28invFigz r,

5. The two posts are "is'ftubi nrin' section-.inclthei;crosgectinallnea is's'ilh, l vibratingtorsionallyyas will ause'th'eiletera'rmto lia-rea natural 4frequencylVofyfvfibra- 9o tion whichiSA'ruv' higlr, high lenough 'gothnt when the o'th''l'bartswoflthei' v"b titty-.SYS- tem arr connoctrdv'to i thepvhol v\\-':illha,ve the high'frequeoy-ab 'v refe Y "B'y making thel` torsion'allyl tions tubular, they` mayv be larger 'dialnotert-l n'i ot' thoirlarger tlu n? bend lateralljY than .ii'oul case. although onie li harm, proileil'the n bending movement i arm .16 ma)7 'either lie the hub portioafor, eepa'ratel If formed sepai'atelygit uns the hubfportion 'ii'ithf la tit 'so thatA therel ian'he tween the?v l'effr aridxita` oi` lever its'elf''slj-longifiiltlih explained. 'so asf to' be emnldidi event,V Va lu' :inn of' lightness to the-face 1- l romp'riees ,V electrodes, .Y granules 4of vowel sounds, and thereby the repeater becomes capable of transmitting telephonie voice currents without'causing any appreciable ldistortion of. the wave forms such as commonly occurs Where-.the vibratory member responds dlsproportionately'- to on'e of vthe prominent frequencies olf-human speech.

There is special :advantage in making the natural frequency of the vsystemabout 1 000 because human specchi doesnot contain any prominent sounds of this frequency and the only resonance eiiect will be a tendency to stronger. response to. the upper part of the range of frequencies characteristic of the vowel sounds say froml 600 to 900 per second.

- This" resonant response 1= is progressively greater for theylii'gher of these-frequencies and .these .arethe'very frequencies which are? most attenuated on long lines.

-quently,1.vhi1 ethe instrument does not actu- Consel ally preventftheunequal', distorting losses on the line, it doescompensate for them by respondingmost strongly to the frequencies which haveA suifered most in transmission.

By actual' test, it has been found. that' Where instrumentsproperly designed in accord an'ce'with. my present invention, are located at Aproper. distances from the sending station, the reproduced vowel waveforms are substantially afs perfect asifthere had ,been

no unequal attenua-tion ofthe higher frequencie's, and the resultingefl'ectis substantially that of distortionless. transmission.

From `the description gg-ivezmthe principle of the' invention and the manner of. applying itto other-forms of instruments.. lvvill now be apparent; It need only be. added that the torsion member may have greater or less length' between .points ofvattachnient, or greater or less cross sectional area,.aocordi1 1g to the frequencycharacteristics it desired that it or they shallimpart tothe other parts of :the system. .Generally speaking, .the shorter'the length. Aand ,greaterV the diameter the higher Wi'll be the frequency, andthe' w maker will proportion these'. factors so that the desired result will be: gained with a minimum degree of stiffness, thus .promoting i the sensibility of the. instrument ns'above explained.v The torsion members may befput under initial,.permanent stress if' desired' by manipulating .the nuts 29 'one Vway v'or the other, although this 'is not necessai tends to'ncrease the work to befper'o. I

in moving the system, In 4such cas.; the initial stress in'one membermay counteract that of the other, producing a static equilibrium when the .parts -are at rest, ndi such condition may operatevto increase the requency of the-.system as a Whole and may be used" for that. purpose, In case or :the repeater, and also to some extent inthe trans mitter, the torsionally-vibrating members .having a -vibratoryfsystem including an arm.

'l'ier connected to such means andA impressing.

manent magnets, to produce a' substantial balance of magnetic attraction on opposite si des The double acting'or two-part microphone cell eontributesft-o the symmetryof the vibratory motion since thereby the' physic a'l resist-ance tomovement'ilr either direc'- ltion is madeapproximntely equaL-s-amat ter of importance when the extent of vibratory motion-is smalLl ielaimf .-5 A

1. An instrument-of the kind described '90 supported on a. member resisting vibration by itsfelastic resistance 'to torsion'and. such resistance bei-ng suiiicient to impart .to the system as aj'whole 'a frequency helov the limit of eludibility but inexcess of the free quency of the highest resonance period. of vowel sounds. 2. *An* instrument. of the kind 'describedhii-.ving a `vibratory system r 'including a' rod vor'n'xe1r1beriXed-'at both endsjand subject to torsion 'by force applied between its ends 1 and having a torsional resistance suited' to give a natural frequency to the said system as a' Whole, beloiy. the limit of '.audibility but in' eic'zessl of the resonance region 'of von-'el sounds.' A f 3. A telephonie'transmitting device* comi -prsing amicrophone cell, means lconnected therewith to .operate it and a torsion A.memJ

theroon a natural frequency period below limit" of'aiulibiiity but higher thanthe highest resonance region voi' vowel sounds.

' 45A transmittingmeans for' telephonie apparatus comprising a microphone, means for operating the same, comprising a'ievclr, said nefans and lever: having a natural fre. ,-'qnency above i000 vibrations per second and seid 4microl-ihone' lever and. parts thereof hav I ingzg only one resonance ,region below' 2(200 vibrationspm second, in. combination with means for fooi-:ratingsaid parts by human' speech Waves.V f F. In a telephone repeater, the combina; tion of-opposed electromug11ets, a, variable resistance medi um located between sai d mag- 'nets and havingr .relatively movable electrodes, one' 'of said electrodes having` an a-lmature on each lside thereof, and torsion4 means for imparting to the `movable system.

' tiontof :opposed electro-xna a natural frequency below the limit of audibility ybut in exeesa of the frequency of the highest resonance period of vowel sounds.

6. In a telephone repeater, the combinaets, a variable between said resistance medium locate' magnets and having a stationar f electrode and a. movable electrode provid with armatures on tpposite sides' thereof, und tor sion means or impartingto the movable system a natural requency below the limit 'of audibility but in exoess of the frequency of the highest resonance period of vowel sounds.

7. telephone repeater comprising an excitin field, a double-actin microphone and a vi ratory system inclu ing two torsion members, each underpermanent stress and counteraoting each other, said torsion members im't arting to the system a natural frequency. lou 'the limitI of audibility but in excess. of `the highest resonance period of voivel',sounds.

8. n" instrument for utilizing Complex frequency. variations characteristic of huf man voice' waves, said instrument having a 40' in colnbiluition with means for applyingrto said system, the complex variations characteristic of human speech.

9. Ai instrument for utilizing complexv frequency lvariations characteristic of human voice waves, said instrument having a v1bratory system of which one of the members comprises an elastic torsion shaft or pivot substantiall inflexible transversely of its axis and a lever element substantially ri 'd transversely of its length whereby oecilliitor` Amovements of said lever are unitary an are confined to arcs having said axis as being sufficient to impart to the 'system as a ivhole a natural frequency far below the limit of audibility but substantially higher than the highest important resonant frequency characteristic of the vowel sounds, in combination with means forapplying to said system, complex variations of various frequencies substantially different from the sai natural frequency of said vibratory system.

10. An instrument for utilizin frequency variations characteristic of human voice waves, said instrument having a vibrntory system of which one of the 'niembers comprises an elastic torsion shaft or pivot, rigidly secured at both ends and sub stantially inflexible transversely of itsaxis, together with a lever element rigidly secured thereto and substantially rigid transversely of its length, whowby osillatory movements of said lever elementl are unitary and are confined to arcs having said axis as a center, the torsional resilience of shaft or pivot being sulliciexit to iin nrt tothe s vstem-as a whole' u natural requeney below the limit of audibility but higher-'than tbc highest important resonant frequency char ncteristie of the vowel sounds, in fcombimu tion u'ithnieans for appl ing to saidsystem, complex variations o various 'frequen4 aies all substantially ditl'erent .from the-said natural frequency of said vibratory system.

In testimony whereof, have signed this specification in the nessus. i

I ELWOOD GRISSINGER.

'itnesses:

FaAvnmN R. Baou'x, DANL. Vv. EMERLING.

coni plex 'a center, the torsional resilience of said pivot 

